1. Technical Field
The invention relates to air suspension systems and in particular to an air suspension system used for vehicles. More particularly, the invention relates to air suspension systems having an auxiliary air reservoir formed by a second air spring which communicates with the air chamber of the vehicle air spring to enable the rate of the vehicle air spring to be varied by adjusting the volume of air in the auxiliary reservoir of the second air spring.
2. Background Information
Air springs have been used for a considerable number of years for various applications, including use in vehicles for absorbing road shock imparted onto the wheels of a vehicle upon the wheel encountering a projection or depression in the roadway. Some examples of such air springs are shown in U.S. Pat. Nos. 4,564,177, 4,718,650, 4,787,606 and 4,787,608.
Each air spring will have a specific spring rate depending upon the design of the air spring components which will provide various ride characteristics for the vehicle on which the particular air spring is mounted. One of the factors which determines the spring rate is the volume of air contained within the flexible sleeve or bellows of the air spring. Varying the volume of air in the flexible sleeve of the air spring enables various spring rates to be achieved. This is presently being accomplished by various means, such as by supplying or removing air into or from the air spring through various control valves, and by the use of auxiliary air reservoirs which are fluidly connected to the vehicle air spring, which air spring is mounted on and extends between spaced structural members of the vehicle. Thus, when a vehicle wheel encounters a depression or projection in the roadway, air will be introduced into or removed from the vehicle air spring by means of the auxiliary reservoir to change the volume of air within the vehicle air spring, thereby changing the spring rate in order to provide the desired ride characteristics for the vehicle.
Heretofore, these auxiliary air springs usually consisted of a rigid canister mounted remotely from the vehicle air spring and connected thereto by a hose or other fluid communication lines. Those canisters generally contained various means for adjusting the volume of the air chamber within the canister, such as a slidably mounted piston.
Examples of such prior art air springs containing auxiliary reservoirs are shown in the following U.S. patents.
Hunt, U.S. Pat. No. 2,115,072 shows a very early air spring having an auxiliary reservoir formed of a solid container with an internally movable piston member. In this arrangement, the spring rate of the suspension system is varied by use of a valve and pump that automatically allows, in accordance with the load on the vehicle, alteration of the spring rate by allowing air to be moved back and forth between the air spring and reservoir.
Van Zijp, U.S. Pat. No. 3,039,761 discloses another air spring having a pair of reservoirs arranged in a series circuit relationship with the air spring. Each of these reservoirs has a fluid passage which communicates with the air spring that contains a mass of porous material which affords a flow area of different size in each passage for affecting the damping of the air spring.
Vander Laan, U.S. Pat. No. 4,159,105 discloses a shock absorber having an adjustable spring load wherein fluid can be pumped from a reservoir into an area of the shock absorber to compress the spring for preload by use of a rigid cylinder and manually operated pump which moves a piston within the cylinder, to affect the transfer of air or fluid into the shock absorber.
Yokoya, U.S. Pat. No. 4,592,540 discloses a Macpherson type strut air suspension system which has an adjustable spring rate wherein there are primary and secondary air chambers in the unit, rather than a separate reservoir.
Karnopp, U.S. Pat. No. 4,743,000 is believed to be the closest known prior art to the present invention. This patent discloses an air spring having an auxiliary reservoir connected thereto, wherein a piston is movable within a rigid cylinder which forms the auxiliary reservoir by means of a drive member. In this system, a rapid switchover valve mounted between the air spring and reservoir, is used to control the pressure of the system.
None of the prior art air suspension systems using auxiliary reservoirs of which I am aware, forms the reservoir from another air spring member, wherein the auxiliary air chamber is formed by the flexible bellows or sleeve of the air spring which extends between a pair of end members, one of which is a piston, and in which the piston is moved by an actuator to control the volume of air within the auxiliary air chamber, the latter being in direct fluid communication with the air chamber of the vehicle air spring.
The use of a second air spring member containing a flexible bellows, in contrast to the rigid canister of prior art air suspension systems, provides for a savings in weight, increases the life of the suspension system by eliminating the use of seals required in the rigid air reservoirs containing sliding pistons, and enables a readily available component to be used thereby reducing the cost of the system components.